Systems and Methods for Self-Cleaning Solar Panels Using an Electrodynamic Shield

ABSTRACT

Systems and methods for self-cleaning a surface of an object where an electrodynamic shield is mounted to a surface of the object. The electrodynamic shield includes one or more sets of electrodes atop a substrate, at least one or more sets of electrodes being covered in a protective film. A coating is applied to the top surface of the protection film. A signal pulse generator is connected to the one or more sets of electrodes. The signal pulse generator generates a pulse signal that causes the one or more sets of electrodes to generate an electric field. The pulse signal comprises a plurality of different pulse signals which have phase differences between consecutive signals, and the electric field causes a particle atop the coating to experience an electrostatic force and be repelled away from the coating. These pulse signals (including shapes, amplitudes, shifts, and frequencies) can be tuned to increase efficiency of removal depending on dust type and relative humidity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the benefit ofpriority to, U.S. Pat. Application No. 16/646,193 filed on Mar. 11,2020, which is a U.S. National Phase Application under 35 U.S.C. 371 ofInternational Application No. PCT/US2018/050321 filed on Sep. 11, 2018,which claims priority to U.S. Provisional Pat. Application No.62/557,070 filed on Sep. 11, 2017, the entire disclosures of which areexpressly incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to equipment for cleaning solarpanels. More specifically, the present disclosure relates to systems andmethods for self-cleaning solar panels using an electrodynamic shield.

RELATED ART

In the renewable energy field, solar power generation using solar panelshas gained widespread interest and increased adoption. A major challengewith existing solar panels is the reduction of output power due to dustand other particles covering the solar panel. Dust deposition on thesolar panels can significantly reduce power output. The standardapproach to alleviate this problem is to mechanically clean the solarpanels, which requires the use of water and manual labor, or water andvery expensive and error-prone robotics. Emerging approaches include theapplication of either hydrophobic or hydrophilic coatings to glasssurfaces of the solar panels, as well as using robots to automate manualcleaning. However, repetitive mechanical cleaning can damage the glasssurfaces of the solar panels while requiring vast amounts of water,which is a scarce commodity in desert regions.

Further approaches include the use of an electrodynamic shield, or“EDS.” The EDS, via electrodes, generates an electric field that causesdust particles on the solar panels to experience an electrostatic force,and to be repelled from the solar panels. Use of the EDS has garneredinterest in order to address dust accumulation problems on solar panelsof vehicles operating on the Moon and on Mars. In the case of the Moon,a low gravity, zero magnetic field, and hard vacuum environment allowthe EDS to repel dust particles.. However, the EDS technique in itscurrent embodiment is not practical for terrestrial applications, due tothe Earth’s humidity levels and low transparencies of electrodematerials currently in use. Specifically, any layer of moisturecondensing on the surface of the solar panel will shield the electricfield and also act as a trap for dust particles due to the resistantforces of the moisture layer, such as dielectrophoresis forces, adhesionforces, etc. Further, with the current EDS systems, particles remain atthe vicinities of electrode edges and at the middle position on top ofthe electrodes. These remaining particles are difficult to repel off thesolar panel, even with additional electric field motivation. Acombination of moisture and dust can also cause highly adhesive dust‘cake’ formation, which is impossible to remove by the current EDSsystems.

Accordingly, the systems and methods disclosed herein solve these andother needs by providing systems and methods for self-cleaning that donot require water or mechanical cleaning, and which addresses themoisture layer problem noted above. Specifically, the systems andmethods disclosed herein solve these and other needs with a novelelectrode and insulator configuration to control water adsorption, andwith a novel electric pulse generator that improves cleaning efficiencyand requires minimal power consumption.

SUMMARY

This present disclosure relates to systems and methods for self-cleaningsolar panels using an electrodynamic shield. The system includes anelectrodynamic shield (“EDS”), which contains one or more sets ofelectrodes, a protective film on the electrodes, a coating atop theprotective film, and a substrate below the electrodes. The electrodesand the protective film are shaped and arranged to control wateradsorption on the surface of the electrodynamic shield. The substratecan be a low iron soda-lime glass cover of a solar panel, which is oneof the most suitable types of glass for the EDS applications. A pulsesignal generator can produce a pulse signal which powers the set(s) ofelectrodes. The pulse signal includes a plurality of different pulsesignals which have phase differences between consecutive signals. Thepulse signals can include different waveforms, amplitudes, andfrequencies. The pulse signal can be enhanced by a leading-edge andtrailing-edge pulses, if desired. The initial pulse can provide ameasurable increase in force to overcome stiction and inertia of thefixed dust particle and to reduce the net power consumed by reducing theamplitude of the subsequent pulses . A combination of pulses can betuned for specific types of dust. The pulse signal generator, whenconnected to a single electrode set, generates an electric field using astanding-wave signal pattern. When connected to multiple electrode sets,the pulse signal generator generates an electric field using atraveling-wave signal pattern. By powering the set(s) of electrodes, theEDS generates an electric field that causes dust particles on thecoating to experience significant electrostatic force. The electrostaticforce combined with gravity cause the dust particles to be repelled offthe solar panel. The sequence of pulses, in combination with thehydrophobic nature of the top coating, loosen the dust particle from thedust cake on the solar panel, which is formed due to presence ofmoisture. Therefore, the EDS described in the invention can clean solarpanels exposed to different types of dust and environmental conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will be apparent from thefollowing Detailed Description of the Invention, taken in connectionwith the accompanying drawings, in which:

FIG. 1 is a diagram illustrating the overall system of the presentdisclosure;

FIGS. 2-3 are diagrams illustrating the electrodynamic shield (“EDS”) ofthe present disclosure, integrated with a solar panel;

FIG. 4 is an illustration showing an example of the electrodes of theEDS arranged into two sets and connected to a pulse signal generator;

FIG. 5 is an illustration showing a cross-sectional view of the EDS ofFIG. 4 , including two sets of electrodes connected to the pulse signalgenerator generating a single standing-wave pulse signal;

FIG. 6 is an illustration showing an example of the electrodes of theEDS arranged into four sets and connected to a pulse signal generator;

FIG. 7 illustration showing a cross-sectional view of the EDS of FIG. 6, including four sets of electrodes connected to the pulse singlegenerator which generates the traveling-wave pattern via the fourseparate pulse signals;

FIG. 8 is a schematic circuit diagram of the pulse signal generator ofthe present disclosure;

FIG. 9 is a diagram illustrating four different pulse signals generatedby the system, wherein each pulse signal is shifted 90° in-phase signal;

FIG. 10 is a photo of oscilloscope traces of the four different pulsesignals;

FIGS. 11A-B are diagrams showing dust particles being removed from thesurface of the EDS;

FIG. 12 is a flowchart illustrating process steps carried out by thesystem of the present disclosure;

FIG. 13 is a diagram showing a cover with a power optimizer, a fixedbase, a bypass connector, and a cover for a standard junction box;

FIG. 14 is a photo of a circuit implementation of the pulse signalgenerator; and

FIG. 15 is a diagram showing various types of dust that were tested.

DETAILED DESCRIPTION

The present disclosure relates to systems and methods for self-cleaningsolar panels using an electrodynamic shield, as described in detailbelow in connection with FIGS. 1-15 .

It should first be noted that the systems and methods will be discussedbelow with reference to a solar panel. However, it is noted that thesystems and methods of the present disclosure can be used with anysystem, including but not limited to, windows, vehicle surfaces, vehiclewindshields, optical devices, etc., such that the electrodynamic shieldallows for automatic cleaning of such objects.

FIG. 1 is a diagram illustrating the overall system, indicated generallyat 10 (hereafter “electrodynamic shield 10” or “EDS 10”). Theelectrodynamic shield 10 includes one or more electrodes 12, aprotection film 14, a coating 16, and a substrate 18. The electrodes 12could be embedded within the protection film 14. The protection film ismade of a material that prevents electrode breakdown. In an example, theprotection film 14 is a transparent and highly dielectric silicondioxide (“SiO₂”). SiO₂ prevents breakdown between the electrodes 12 at ahigh voltage. Further, SiO₂ protects the electrodes 12 from theenvironment and environmental elements. Specifically, the properties ofSiO₂ allow for scratch resistance, moisture resistance, hightransparency, etc. Those skilled in the art would understand that othermaterials can be used as the protection film 14, if desired, and mayprovide additional or different benefits.

The EDS 10 generates an electric field that causes dust particle(s) 20to experience an electrostatic force with two vector componentdirections F_(x) and F_(y) and be repelled from the EDS 10.Gravitational forces G, which are continuously acting on the dustparticle 20, help the dust particle 20 move towards the ground with aresulting particle trajectory T.

In a first example, the electrodes 12 are made of transparent Indium TinOxide (“ITO”). ITO is a transparent material with superior transparency,conductivity, and durability properties. The transparency of ITO canreach higher than 90%. In a second example, the electrodes 12 are madeof Florine doped Tin Oxide (“FTO”). FTO is a transparent conductiveoxide (“TCO”) of properties comparable to ITO. Those skilled in the artwould understand that other transparent materials can be used to producethe electrodes, if desired, and may provide additional or differentbenefits.

In an example, the width of the electrodes 12 is in a range of 0.1 to100 micrometers (“um”) and the inter-electrode spacing is in a range of0.1 to 100 um. It should be noted that these ranges are only used asexamples, and other ranges can be used. In another example, the width ofthe electrodes is in a range of 10 um to 400 um and the inter-electrodespacing is in a range of 10 um to 800 um. The geometry of the electrodeis dependent upon the types of dust to be cleaned. For different typesof dust, the efficiency depends upon different inter-electrode spacingand electrode shapes. The efficiency of the electrode is based on thebalance between the sheet resistance and transparency of the electrodes.

The optically transparent coating 16 is applied to the top surface ofthe protection film 14. The coating 16 has one or more materialproperties, including but not limited to, anti-reflective properties,hydrophobic properties, etc. The material properties allow the coatingto function efficiently under different conditions, such as, forexample, high relative humidity. As such, the coating 16 enables theapplication of the EDS 10 in high humidity areas. The surface topologyof the coating 16 can be altered to trap light inside and prevent lossof light due to reflection. One skilled in the art would understand howto tune the surface topology depending upon dust conditions in anapplicable area.

The substrate 18 can be a rigid substrate and/or a flexible substrate. Aflexible substrate can include flexible polymeric substrates such as anethylene vinyl acetate (“EVA”) film, a polyethylene terephthalate(“PET”) film, a Polytetrafluoroethylene (“PTFE”) film, etc. The rigidsubstrate can include rigid low iron soda-lime glass substrates, solarpanels, windows, automotive windshields, optical devices, and othersubstrates.

The EDS 10 is integrated with a solar panel. In an example, the EDS 10can be integrated as the top layer of the solar panel. However, thoseskilled in the art would understand how to integrate the EDS 10 as anylayer of the solar panel. FIG. 2 is an illustration showing the EDS 10integrated with a crystalline solar panel (“CSP”) 22. FIG. 3 is anillustration showing the EDS 10 integrated with a thin film solar panel(“TFSP”) 24. It should be understood that the CSP and the TFSP are onlyexamples of solar panels, and the EDS 10 can be integrated with any typeof solar panel. It should also be understood that the EDS 10 is notlimited to being used with only solar panels, and can be used with otherapplications, such as, but not limited to, windows, vehicle surfaces,vehicle windshields, optical devices, etc.

The electrodes 12 are grouped into one or more sets of electrodes. Theone or more sets of electrodes can be organized into differentconfigurations and connected to a pulse signal generator. Depending onthe arrangement, different wave patterns can be generated in theelectrode sets. FIG. 4 is an illustration showing a first example of theelectrodes arranged into two sets 32, 34 and connected to a pulse signalgenerator 36. A pulse signal 38 from the pulse signal generator 36powers the two sets of electrodes 32, 34 and generates a standing-wavepulse signal. More specifically, the pulse signal 38 powers the two setsof electrodes 32, 34 to generate an electric field that will charge thedust particles 20 and levitate them away (e.g., repel) from the surfaceof the EDS 10. It should be understood that solar panels are generallyinstalled with a tilt angle (e.g., 25° - 30°), and the gravitationalforce will aid in gliding the levitated dust particles 10 off thesurface of the EDS 10.

FIG. 5 is an illustration showing a cross-sectional view of the EDS 10of FIG. 4 , connected to the pulse signal generator 36 for generating asingle standing-wave pulse signal. The EDS 10 also includes the coating16 on the topmost surface, the protective film 14 used to prevent theelectrodes 12 from the electrical breakdown, and the substrate 18 (e.g.,a low iron soda-lime glass cover substrate of the solar panel).

FIG. 6 is an illustration showing a second example of the electrodesarranged into four sets 42, 44, 46, 48 connected to the pulse signalgenerator 36. A pulse signal from the pulse signal generator 36 powersthe four sets of electrodes 42, 44, 46, 48 and generates atraveling-wave pattern. More specifically, the pulse signal powers thefour sets of electrodes 42, 44, 46, 48 with four separate pulse signals52, 54, 56, 58. The four separate pulse signals 52, 54, 56, 58 havephase differences of 90° between consecutive signals. This form ofelectrode arrangement (four sets of electrodes and a traveling-wavepattern) will slide the dust particles 20 towards the edge of the EDS 10surface and onto the ground.

FIG. 7 is an illustration showing a cross-sectional view of the EDS 10of FIG. 6 , connected to the pulse single generator 36 which generatesthe traveling-wave pattern via the four separate pulse signals 52, 54,56, 58. It should be understood that the generation of standing wavesand traveling waves by the pulse signal generator is only by way ofexample, and the systems, methods, and embodiments discussed throughoutthis disclosure can generate and use other waves, such as, but notlimited to, triangular waves, sine waves, saw-tooth waves, etc.

FIG. 8 is a schematic circuit diagram of the pulse signal generator 36.Specifically, the schematic diagram shows the pulse signal generator 36generating four different pulse signals 52, 54, 56, 58, which have phasedifferences of 90° between consecutive signals. The pulse signalgenerator 36, when connected to a single electrode set (e.g., electrodeset 32), as shown in FIG. 4 , will generate an electric field using astanding-wave signal pattern. The pulse signal generator 36, whenconnected to the four electrode sets 42, 44, 46, 48, as shown in FIG. 6, will generate an electric field using a traveling-wave signal pattern.The circuit includes a DC power source (“DCPS”) 60, a pulsing unit 62,and four pairs of power switching transistors 66, 68, 70, and 72, whichcould also function as optoisolators for the pulsing unit 62. The DCPStakes power directly from a solar panel as an input 74. The pulsing unitis a computing module that provides commands to the transistors. Eachpair of power switching transistors has a transistor to switch thepositive voltage (“PV”) and another is to switch negative voltage(“NV”). The pulse signal 38 can be a square wave of an amplitude of eachsignal up to a certain voltage. For example, the pulse signal 38 can bea square wave of an amplitude of each signal up to 1500V. FIG. 9 is anillustration showing the different pulse signal 52, 54, 56, and 58 witheach pulse signal being shifted 90° in phase compared to a consecutivesignal. FIG. 10 is a photo of four different pulse signals 52, 54, 56,and 58.

Referring back to FIG. 8 , the sets of electrodes are powered by thepulse signals 38 or 52, 54, 56 and 58. The pulse signals produce anelectrical field on the surface of the coating 16 and remove theparticles from the surface of the solar panel. The pulse signals, whenconnected to a different arrangement of the sets of electrodes, willremove particles via a different methodology. Furthermore, the EDS 10containing an arrangement of two sets of electrodes 32, 34, asillustrated in FIG. 5 , will levitate the dust particles away from thesurface of the EDS 10 in a hopping manner and the dust particles willreach the ground will the aid of the gravitational force. The EDS 10containing the arrangement of four sets of electrodes 42, 44, 46, 48, asillustrated in FIG. 7 , slides the dust particles in a traveling mannertowards the edge of the panel, and the dust particles will fall on theground. This eliminates or greatly reduces the need for gravitationalassistance. In this manner, substrate surfaces perpendicular to theforce of gravity can also be cleaned.

The pulse signal generator 36 can adjust the signal parameters of thepulse signals. The signal parameters include an amplitude of the signal,a frequency of the signal, etc. The amplitude of the signal and thefrequency of the signal required to clean the dust particles 20 aredetermined by the properties of the dust particles 20, such as, but notlimited to, a dust particle size, a dust particle chemical composition,and a dust particle surface charge density. Adjusting the signalparameters adjusts the electric field strength, which removes the dustparticles from the surface of the EDS 10. Specifically, the electricfield strength is adjusted based on the amplitude of the pulse signals,and the particle charging and removing process is adjusted based on thefrequency of the pulse signals. In an example, the amplitude is in arange between 400 -1000 volts and the frequency is in a range from 30 to100 Hz. It should be understood that other ranges can also be used.FIGS. 11A - 11B illustrate dust particles being removed from the surfaceof the EDS 10.

It should be understood that the electrostatic force that moves the dustparticles grows as the dust particle size increases and is very weak fora dust particle with a small size, which makes removal of the ultra-fineparticle difficult. Therefore, the dust particle size is required togrow by accretion before switching on the electrostatic force. Theelectrostatic force acting on the dust particle mainly depends on itssize and the gradient of the square of the magnitude of the electricfield. In an example, increasing the electrostatic force acting on thedust particle improves the gradient of the square of the magnitude ofthe electric field by enhancing the strength of the electric field. Theelectric field strengths can be achieved by integrating microelectrodeswith smaller size and, as a result, a low voltage is so strong that therange of the controllable particle size is expanded gradually.

It should further be understood that, for better efficiency, the size ofthe dust particles should be less than the inter-electrode spacing. Theelectrode 12 width and inter-electrode separation should be on the scaleof the smallest dust particle. Therefore, EDS 10 being constructed withsmaller electrode width and inter-electrode spacing in the range of 10to 100 um can be more efficient for a fine dust particle in the range of5-100 um.

In addition to reducing the electrode gap, insulating microstructurescan enhance the strength of the electric field as well. As compared totraditional electrode-exposed devices, external electrodes can beemployed to generate a uniform electric field, and insulatingmicrostructures can be embedded into microchannel to squeeze theelectric field. Thereby, a high electric field gradient with a localmaximum is created. The high electric field gradient has advantages inthat the structure is mechanically robust and chemically inert, and avery high electric field may be applied without air breakdown dischargeor arcing happening at 3 V/um at STP. While the traditionalelectrode-based devices use small amplitude AC signals, high amplitudeDC voltages pulses can be directly applied to blocks to squeeze electricfield to steer the electric field gradient to have a parallel componentto the substrate instead of perpendicular to the substrate.

The dust deposition rate in a typical solar power plant located in thedesert region is 0.3-0.5 g/m² per day. The deposited dust hinders thelight reaching a solar cell(s) on the solar panel. Automated dustremoval of dust can be performed with the addition of a sensor whichresponds to the loss of light reaching the solar cell. An activationsystem, which includes the sensor, can be programmed to activate thepulse signal generator 36 when the sensor detects a predetermined dropin light intensity reaching the solar panel and direct a small amount ofpower from the solar cell to the pulse signal generator 36 to generatethe pulse signals.

FIG. 12 is a flowchart illustrating process steps carried out by thesystem of the present disclosure, indicated generally as method 80. Instep 82, the system determines a first light intensity, where the firstlight intensity is an amount of light reaching the solar cell. In step84, the system determines whether the first light intensity is below afirst predetermined threshold. When the first light intensity is notbelow the first predetermined threshold, the system proceeds to step 82to again determine the first light intensity. The system can againdetermine the first light intensity immediately, or after apredetermined time delay. When the first light intensity is below thefirst predetermined threshold, the system proceeds to step 86, where thesystem activates the EDS 10. The EDS 10, as discussed above, produces anelectrical field on the surface of the coating 16 and removes the dustparticles from the surface of the solar panel. In step 88, the systemdetermines a second light intensity. In step 90, the system determineswhether the second light intensity is below a second predeterminedthreshold. The second predetermined threshold can have the same value asthe first predetermined threshold, or a different value. When the secondlight intensity is below the predetermined threshold, the systemproceeds to step 88, and, again determines a second light intensity. Thesystem can again determine the second light intensity immediately, orafter a predetermined time delay. When the second light intensity is nolonger below the second predetermined threshold, the system proceeds tostep 92, where the system deactivates the EDS 10.

It should be noted that the electrodes 12 could be activated by eitherusing a standing wave pulse signal or traveling wave pulse signal. Newergeneration solar modules are optionally integrated with a poweroptimizer during the manufacturing process. The circuit used to activateelectrodes can be incorporated into the already existing power optimizerdevice with the few additional steps during the manufacturing process ofthe solar panels.

The power optimizers have the ability to change the voltage or currentto reduce system losses and have similar electronic functions that couldbe extended to incorporate the control in FIG. 8 . The other devices arestring inverters and micro-inverters. Inverters convert direct current(“DC”) energy generated by the solar panels into usable alternatingcurrent (“AC”) energy. Micro-inverters and power optimizers are oftencollectively referred to as Module-Level Power Electronics or MLPEs.MLPE technologies are rapidly gaining popularity and market share astheir costs have come down.

Power optimizers are located at each panel, usually integrated into thepanels themselves. However, instead of converting the DC electricity toAC electricity at the panel site, the DC electricity is conditioned,energy loss optimized and sent to a string or central inverter. Thisapproach results in higher system efficiency than a string inverteralone. It also reduces the impact of individual or sectional panelshading on system performance and offers panel performance monitoring.

The AC/DC converter can be connected by installers to each solar panelor embedded by module manufacturers, replacing the traditional solarjunction box. As such, the circuit shown in FIG. 8 can be directlyintegrated into the power optimizer for the newer solar panel or intothe junction box for the regular solar panel. This integration of thecircuit into the junction box enclosure and power optimizer that isalready embedded into at the back of the solar panel will also provideprotection for water and dust ingression. Moreover, the junction box istypically IP67 certified, which ensures safe operation even in a harshcondition such as dust storm, high temperature, and high humidity. FIG.13 is an illustration showing a cover with a power optimizer 102, afixed base 104, a bypass connector 106, and a cover for a standardjunction box 108. As discussed above, the circuit shown in FIG. 8 can bedirectly integrated into the power optimizer 102 or into the fixed base104, and covered by the standard junction box cover 108.

FIG. 14 is a photo showing a circuit implementation of the pulse signalgenerator. As can be seen, FIG. 14 includes a transformer, a bridgerectifier 114, a microcontroller board 116, and a plurality ofintegrated circuits and discrete components on a breadboard 118. Thecircuit implementation can be integrated into integrated into the poweroptimizer 102 or into the fixed base 104 of FIG. 13 .

FIG. 15 is a photo showing various types of dust used for testing,including : nonporous mineral dust, porous mineral dust, hydrophobicorganic dust, and hydrophilic organic dust. It was discovered thatdifferent types of dust require a different combination of amplitude,phase shifts and frequency of the pulse signal. The coating 16 with thehydrophobic properties helps the EDS 10 to clean even the mosthygroscopic dust.

Having thus described the system and method in detail, it is to beunderstood that the foregoing description is not intended to limit thespirit or scope thereof. It will be understood that the embodiments ofthe present disclosure described herein are merely exemplary and that aperson skilled in the art can make any variations and modificationwithout departing from the spirit and scope of the disclosure. All suchvariations and modifications, including those discussed above, areintended to be included within the scope of the disclosure. What isintended to be protected by Letters Patent is set forth in the followingclaims.

What is claimed is:
 1. A system for self-cleaning a surface of anobject, comprising: an electrodynamic shield mounted to a surface of theobject, the electrodynamic shield including one or more sets ofelectrodes atop a substrate, the at least one or more sets of electrodescovered in a protective film, and a coating applied to the top surfaceof the protection film; and a signal pulse generator connected to theone or more sets of electrodes, wherein the signal pulse generatorgenerates a pulse signal that causes the one or more sets of electrodesto generate an electric field, wherein the pulse signal comprises aplurality of different pulse signals having phase differences betweenconsecutive signals, and wherein the electric field causes a particleatop the coating to experience an electrostatic force and be repelledaway from the coating.